1. Field of the Invention
The present invention relates to a tomosynthesis radiographing apparatus for radiographing a tomographic image of a subject.
2. Description of the Related Art
The use of a Talbot interferometer, which produces Talbot effect by a diffraction grating and generates Moire fringes in combination with another diffraction grating, in X-ray applications has been studied as described, for example, in U.S. Pat. No. 5,812,629 (Patent Document 1) and U.S. Pat. No. 7,180,979 (Patent Document 2).
Patent Document 1 or Patent Document 2 proposes an X-ray radiographing apparatus having an X-ray source, two diffraction gratings, and an X-ray image detector, in which the two diffraction gratings and X-ray image detector are formed on a planar substrate.
Where parallel beam, such as synchrotron radiation is used, the planar shape described above does not pose any problems, but it gives rise to a problem in medical diagnostic applications and the like in which an X-ray source that radiates widely spreading beams is generally used. That is, X-rays pass through the diffraction gratings at a center portion without any difficulty, but at a portion other than the center portion, X-rays are blocked by diffraction members and unable to pass through the diffraction gratings because the X-rays are incident from oblique directions. For example, Japanese Unexamined Patent Publication No. 2006-259264 (Patent Document 3) proposes an amplitude diffraction grating in which metal X-ray absorption members, each having a width of 2 to 10 μm and a thickness of 25 to 100 μm, are disposed at an equal interval of 2 to 10 μm. It can be thought that the use of such a diffraction grating may possibly cause the problem described above. Accordingly, large-size X-ray phase imaging has been difficult in medical diagnostic applications.
Consequently, Japanese Unexamined Patent Publication No. 2007-206075 (Patent Document 4) proposes an X-ray radiographing apparatus in which a diffraction grating strip is formed so as not to shade the optical path of a beam.
Further, Japanese Unexamined Patent Publication No. 2007-203063 (Patent Document 5) describes an X-ray radiographing apparatus having a detection element formed of multiple of elongated detection strips disposed parallel to the grid line of a phase diffraction grating. According to the X-ray radiographing apparatus, a single measurement with each beam allows a phase image to be obtained, reducing the number of required measurements. Still further, Japanese Unexamined Patent Publication No. 2007-203062 (Patent Document 6) proposes an x-ray radiographing apparatus for obtaining a phase image, as in Patent Document 5, and has a scintillation strip.
In the mean time, a radiographing apparatus having an X-ray emission unit in which multiple of X-ray sources are spatially distributed is proposed as described, for example, in U.S. Patent Application Publication No. 20070133747 (Patent Document 7) or U.S. Patent Application Publication No. 20070009088 (Patent Document 8). The apparatus allows X-ray imaging in which the influence of scattered X-rays are eliminated by combining images obtained by emitting X-rays outputted from each X-ray source.
Here, for example, if the distributed X-ray sources described in Patent Documents 7 and 8 are applied to one of the X-ray radiographing apparatuses described in Patent documents 1 to 6, the exposure range of a beam outputted from each X-ray source can be reduced, whereby the problem that a beam can not pass through a diffraction grating at a peripheral portion thereof may be avoided.
Use of an X-ray source that emits, for example, a pencil beam as the X-ray source that emits the narrow beam described above, however, multiple X-ray sources are required, when performing large size radiation phase imaging, according to the size, resulting in very low utilization efficiency of the X-ray sources. Further, provision of such a large number of X-ray sources results in a huge amount of heat which requires a large-scale structure for cooling the X-ray sources, leading to a cost increase.
In view of the circumstances described above, it is an object of the present invention to provide a tomosynthesis radiographing apparatus capable of eliminating the influence of scattered radiation and improving the utilization efficiency of a radiation source.